Anthraquinone-1,8-disulfonic acid

An example of a process using O2 to oxidize HiS is the Stretford process, which is licensed by the British Gas Corporation. In this process the gas stream is washed with an aqueous solution of sodium carbonate, sodium vanadate, and anthraquinone disulfonic acid. Figure 7-9 shows a simplified process diagram of the process. 

Stretford A process for removing hydrogen sulfide and organic sulfur compounds from coal gas and general refinery streams by air oxidation to elementary sulfur, using a cyclic process involving an aqueous solution of a vanadium catalyst and anthraquinone disulfonic acid. Developed in the late 1950s by the North West Gas Board (later British Gas) and the Clayton Aniline Company, in Stretford, near Manchester. It is the principle process used today, with over 150 plants licensed in Western countries and at least 100 in China. 

Takahax A variation of the Stretford process for removing hydrogen sulfide from gas streams, in which naphthaquinone sulfonic acid is used in place of anthraquinone disulfonic acid. Four variants have been devised types A and B use ammonia as the alkali, types C and D use sodium hydroxide or carbonate. Developed by the Tokyo Gas Company and licensed in the United States by Ford Baken and Davis, Dallas, TX. Many plants are operating in Japan. 

Absorption-oxidation processes oxidize absorbed H2S directly to elemental sulfur in solution (1). The principal example in current industrial use is the Stretford process (3). The chemistry of the process can be represented by the following idealized equations (ADA represents anthraquinone disulfonic acid) ... 

Stretford plants have been in operation for 30 years. There are hundreds of such plants worldwide, used in a variety of sulfur removal operations (Dalrymple 1989). In a Stretford process, the hydrogen sulfide in the feed gas stream is absorbed and oxidized to elemental sulfur in aqueous phase, using pentavalent vanadium which is subsequently reduced from a pentavalent form to a tetravalent form. Later in the process, the vanadium is re-oxidized back again, using anthraquinone disulfonic acid (ADA) as a catalyst, and the elemental sulfur is floated to the surface of the solution and removed. 

AQ, short for anthraquinone disulfonic acids, see text for details. 

Fig.6. Cyclic voltammetry of 2,6-anthraquinone disulfonic acid at mercury ultramicroelectrodes. Scan rate = 10240 mV/s. The top voltam-mogram was obtained with a platinum electrode overcoated with mercury. The bottom voltammogram was obtained using a platinum electrode that was etched and silanized before coating with mercury as shown in Fig.5.

The first stage of the Stretford process absorbs H2S over sodium carbonate contained in the wash liquor together with sodium ammonium vanadate, anhydrous citric acid and anthraquinone disulfonic acid. The reaction... 

The V ions are re-oxidized to vanadium pentoxide by adding air in the oxidation section, the anthraquinone disulfonic acid acting as oxygen carrier and accelerator. 

Hydrogen sulfide Stretford Sodium caibonate. sodium vanadate, and anthraquinone disulfonic acid... 

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